The present invention relates to power supplies and, more specifically, to an uninterruptable power supply.
Existing uninterruptable power supplies supply back up alternating current to electronic components in the event of normal power interruption. Such power supplies typically include a rechargeable battery, a rectifier circuit for recharging the battery and an inverter for producing alternating current from the battery. They also include a transformer that includes windings for transforming normal service power to a load, auxiliary windings for battery charging, and windings for transforming battery-supplied alternating current to a load. The auxiliary windings add cost and complexity to the power supply. Also, existing power supplies are susceptible to certain damage from battery lead reversal or short-circuit.
Such existing power supplies are typically sold as single units that are bulky to ship and require replacement of the entire unit if a single component fails. The likelihood of component failure is increased as a result of there being a common housing for both the transformer, and the associated electronics. This is because removal of heat from all of the components usually requires a fan that is subject to mechanical failure. Also, a power supply produced as a single unit does not lend itself to upgrading of a single component. Upgrading of electronics occurs relatively frequently because advances in electronics occur relatively frequently, but upgrading of transformers does not occur as frequently because transformer technology does not change as frequently.
Therefore, there is a need for an uninterruptable power supply that uses a single set of windings both for recharging the battery and for supplying inverter power to the transformer. There is also a need for a modular power supply that allows for separate shipping and sale of both the transformer and associated electronics.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is an uninterruptable power supply with an external or internal rechargeable battery having a positive terminal and a negative terminal, and a transformer. The transformer includes: a battery side transformer winding having a first terminal, a second terminal and a third terminal; a load side transformer winding inductively coupled to the battery side transformer winding via a core; and a power supply side transformer winding that is inductively coupled to the battery side transformer winding via the core. An inverter circuit couples the positive terminal of the battery to the first terminal of the battery side transformer winding and couples the negative terminal of the battery to the second terminal and the third terminal of the battery side transformer winding. The inverter circuit includes a switching circuit that forms a bridge rectifier circuit that allows current from the battery side transformer winding to flow in only one direction into the battery when the switching circuit is in a first switching state (operating from mains) so that current from the power supply side transformer winding induces an alternating current in the battery side transformer winding that passes through the bridge circuit to generate a direct current that charges the battery when the switching circuit is in the first switching state. The switching circuit also forms a push-pull inverter circuit that generates an alternating current from a direct current supplied by the battery when the switching circuit is in a second switching state (operating from batteries), thereby inducing an alternating current in the load side transformer winding. A control circuit drives the switching circuit into the first switching state when at least a predetermined power level is supplied to the power side transformer winding. The control circuit also drives the switching circuit into the second switching state when less than the predetermined power level is supplied to the power side transformer winding. Aside from the reduction in transformer windings, the mode switching circuit provides protection from battery lead reversal or short-circuits, such as may occur during installation or maintenance.
In another aspect, the invention is an uninterruptable power supply that includes a transformer module that is disposed in a first enclosure. The transformer module includes a transformer that is couplable to both a charging power source and a load. The first enclosure includes a first interior wall with a first electrical connector affixed thereto. The first electrical connector is electrically coupled to a battery side winding of the transformer. The uninterruptable power supply also includes an electronics module disposed in a second enclosure different from the first enclosure. The second enclosure includes a second interior wall that is complementary in shape to the first interior wall. The electronics module interfaces to an internal or external rechargeable battery that is capable of supplying a direct current. The module includes an inverter, electrically coupled to the battery, that is capable of generating an alternating current from the direct current; a recharging circuit that is capable of selectively providing direct current to the battery; and a second electrical connector, affixed to the second interior wall and complementary to the first electrical connector. The second electrical connector is electrically coupled to both the inverter and the recharging circuit so that both the inverter and the recharging circuit may be electrically coupled to the battery side winding of the transformer by physically coupling the first electrical connector to the second electrical connector.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.